diff --git a/langfuse/callback/langchain.py b/langfuse/callback/langchain.py
index 5b41fa1a0..ef6a63e2c 100644
--- a/langfuse/callback/langchain.py
+++ b/langfuse/callback/langchain.py
@@ -56,10 +56,12 @@
 
 try:
     from langgraph.errors import GraphBubbleUp
+
     CONTROL_FLOW_EXCEPTION_TYPES.add(GraphBubbleUp)
 except ImportError:
     pass
 
+
 class LangchainCallbackHandler(
     LangchainBaseCallbackHandler, LangfuseBaseCallbackHandler
 ):
@@ -1173,6 +1175,16 @@ def _parse_usage_model(usage: typing.Union[pydantic.BaseModel, dict]):
                         "token_count"
                     ]
 
+    usage_model = (
+        {
+            k: v
+            for k, v in usage_model.items()
+            if v is not None and not isinstance(v, str)
+        }
+        if isinstance(usage_model, dict)
+        else usage_model
+    )
+
     return usage_model if usage_model else None
 
 
diff --git a/langfuse/extract_model.py b/langfuse/extract_model.py
index 192522846..5880e9624 100644
--- a/langfuse/extract_model.py
+++ b/langfuse/extract_model.py
@@ -106,7 +106,10 @@ def _extract_model_name(
 
 
 def _extract_model_from_repr_by_pattern(
-    id: str, serialized: Optional[Dict[str, Any]], pattern: str, default: Optional[str] = None
+    id: str,
+    serialized: Optional[Dict[str, Any]],
+    pattern: str,
+    default: Optional[str] = None,
 ):
     if serialized is None:
         return None